Conventional writers generally use bridge circuits to route current bidirectionally in a two-terminal recording head. As recording speeds have risen to greater than 2 Gb/s, writer drivers have used complementary PNP devices in order to obtain symmetrical bi-directional fast-rise current flow in the write head. Conventional writers are separated from the write element by a transmission line approximately 2 cm in length. Therefore, the transmission line terminates at the sending end in order to reduce data-dependent jitter caused by reflections. Sufficient precharge pulse (or overshoot) is needed to secure a fast rise time for the writer head current. Overshoot is applied to increase transition gradient in the writing process. Such increase is not always necessary in Heat Assisted Magnetic Recording (HAMR) systems which rely on heat modulation to imprint transitions into the medium. In such HAMR systems, which rely on laser radiation to heat the medium, the magnetic field needs to reach steady-state before laser illumination is switched.
Some conventional writers use a SiGe process to secure additional writer performance. Complementary SiGe BiCMOS processes are costly, especially if the PNP device implements a germanium-doped base. Because hole mobility is lower than that of electrons, PNP transistors are inherently slower than NPN devices.
High current transmission lines connecting the writer to the write head use a termination at the writer to prevent interference caused by back-reflection from the head (unless a broadband termination can be designed in the head). This results in losses and a degraded risetime. Broadband termination in the writer is also impaired by shunt capacitances.
It would be desirable to implement a writer that does not use PNP transistors while also providing high data rates and/or lower power consumption.